The present invention relates to the field of measuring electric brain activity and more specifically to the positioning of electrodes on a user's scalp for this purpose.
In order to measure electric brain activity a device is required with electrodes that are in contact with the user's head. Such devices are well known for providing medical diagnostics, for example for electroencephalography (EEG). The main challenge in applying EEG electrodes is to get a low impedance contact to the scalp. In clinical measurements this is normally done with an elastic cap with integrated Ag/AgCl coated metal cups. The skin underneath these cups is usually prepared by degreasing and often additional abrasion, i.e. removal of the dry top layer of the scalp. The cups are filled afterwards with gel. This assures a low ohmic contact to the deeper skin layer and a ‘conversion’ from ionic current in the body to electron current in the measuring system. Using conductive gel also partly solves the problem of the varying distance between the metal contact and the skin due to the variation from person to person of the hair layer thickness.
For non-medical applications like sports and life style consumer products it is not practical to use these kind of ‘wet’ electrodes and perform the skin preparation essential for their function. There are a number of solutions and investigations aiming at realizing ‘dry’ electrodes.
WO 00/45701 discloses such a ‘dry’ electrode solution. It discloses a headgear, which includes a front forehead pad, a base strap assembly connected to the front forehead pad, a plurality of EEG electrode locators for receiving EEG electrodes, and a plurality of locator straps connected to the front pad of material, the base trap assembly, and to the plurality of EEG electrode locators for accurately positioning the plurality of EEG electrode locators positioned relative to the scalp of a user. A visor can be attached to the front pad of material, and the base strap assembly may include an occipital locator device. A plunger assembly with spreadable fingers for optionally parting the hair of the user's scalp is also provided that is inserted in the electrode locators to optionally prepare the user's scalp and to seat the electrodes. However, the headgear according to this publication requires that a user pushes each plunger assembly into contact with the scalp. So, the user needs to re-set the plunger assemblies to the initial positions every time the headgear is taken on and off.